APES 4.9 El Nino and La Nina

  • ENSO (El Nino - Southern Oscillation) is a regular event that occurs every 3-7 years, beginning in December
  • ENSO takes place in the southern Pacific Ocean, between Australia and South America
  • Changes in atmospheric winds and ocean currents play a part in ENSO, and it effects associated terrestrial areas
  • Normal wind patterns blow from east (South America) to west (Australia)
    • These are the easterlies/easterly trade winds
  • During El Nino, winds stall
    • They may reverse and become westerlies
    • The position of cloud formation also changes as warm air is rising in a different place
  • La Nina is an “enhanced normal”
    • The easterlies are stronger
    • More moisture is driven into the atmosphere
  • In normal conditions, as cold water rises up to the coast of South America, bringing with it lots of nutrients
    • Fish that feed on these nutrients are drawn to these upwellings and thrive off the coast during this time
    • But when the winds and currents stall/reverse, that upwelling isn’t as prominent, and so fish populations migrate or decline
    • Note the economic impacts this will have on South American fishing industries
  • La Nina will have warm water traveling closer to the Australian coast and an intensified upwelling